This invention is a high-powered, portable, hydraulic cutter. It is especially suited for use as a rescue tool, as it is capable of cutting through sheet metal and can thereby extricate victims from the wreckage of accidents. But the invention can also be used for other purposes.
One example of a rescue tool of the prior art is shown in my U.S. Pat. No. 4,531,289. The latter patent shows a hydraulically-operated tool having two cutting blades which open and close upon each other. Another example of a rescue tools having two moving blades is given in U.S. Pat. No. 4,392,263.
The cutters of the prior art, which have two moving blades, are most effective in snapping metallic cables or posts, and in performing other tasks which require only one stroke. But when it is necessary to cut through sheet metal, such as the body of a wrecked automobile, many cutting strokes are needed, and the cutters of the prior art perform poorly. While a cutter having two moving blades can easily make an initial cut in a piece of sheet metal, it is very difficult to make subsequent cuts. The moving blades are joined together at a boss, and the boss prevents the tool from being inserted into an existing cut. In making the second cut through the sheet metal, it is therefore necessary to insert one of the blades through the first cut, from above or below the surface of the metal. Inserting the blade in this manner invariably places the tool in an awkward position, and causes the whole tool to rotate when the blades are pushed together. Any subsequent cut is usually no more than a small "nibble", compared with the length of the initial cut. In an emergency situation, it is important that each cut be as long as possible, so that the tool can cut through the piece of sheet metal as quickly as possible.
When the tool has two moving blades, an equal amount of force must be applied to both blades. The metal is thus cut with equal force from both sides, and will therefore be kept centered while being cut. With two moving blades, the force generated by the hydraulic system must be split between the two blades. This requirement means that the piston and the hydraulic cylinder must be quite large. The cutters of the prior art therefore must be capable of developing a larger amount of power, to develop the same cutting force.
Another disadvantage of cutters having two moving blades is that the blades must be opened fully before removing them from the material being cut. Opening the blades fully consumes additional time, which is precious in a rescue context.
The present invention solves the problems described above with a practical cutting tool having a single moving blade. This single blade cutter allows a second, or continuing, cut to be made easily, due to the structure of the stationary blade. By concentrating the power of the hydraulic system on a single moving blade, it is possible to reduce the area of the piston by about 50%, while maintaining the same output force. This reduction of piston size reduces the overall volume and weight of the entire tool, making it easier to carry and easier to manipulate. The present invention is therefore especially useful in an emergency.